There have been numerous attempts to make use of starch (a plant carbohydrate) as a "natural plastic" in a number of areas. It is important to commercial development that the starches be processible on standard equipment and use existing technology. However, natural starches are relatively grainy and, if they are to be suitably processed, they must first be destructured.
It has long been recognized that amylose, an important component of starch, is soluble in formaldehyde-containing aqueous solutions and alkaline aqueous solutions. In either case, the ultimate solutions obtained are relatively viscous and their stability is based primarily on the concentration of alkali or formaldehyde. Both solutions are suitable for the production of fibers, filaments, or foils.
The production of fibers, filaments, or foils from amylose has been carried out from solution in precipitation baths; i.e. wet spinning. This is set forth in, for example, DE-PS 10 63 325. However, there is no mention in this patent of any thermoplastic method.
In DE-OS 23 62 991, pharmaceutical preparations with delayed release of active ingredients for direct introduction into body cavities, are described. A mixture of the active ingredient and the polymer, including starch among other materials, is processed by melt spinning and extruded; the extrusion is then cut into pellets. These pellets are put into the usual melt spinning apparatus to produce fine fibers. The fibers are cut to a suitable length and carded dry to form "cotton" wads. The melt spinning process is mentioned very generally, but neither the process nor apparatus are not specifically described; only the use of hydroxypropyl cellulose and the extrusion are set forth. This melt spinning process is today the simplest and most widely used method for the production of synthetic filaments.